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Spectrochemical Trace-Element Analysis in Steels and Ferrous Alloys

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Spectrochemical Trace-Element Analysis in Steels and Ferrous Alloys SPECTROCHEMICAL TRACE-ELEMENT ANALYSIS IN STEELS AND FERROUS ALLOYS by JOHN ERIC CHESTER B.Sc, A.R.0 A thesis submitted for the Degree of Doctor of Philosophy of the University of London Department of Chemistry October 1971 Imperial College of Science and Technology London S.W.7 Acknowledgement All work in this thesis is original except where due acknowledgement is made, and was carried out at Imperial College between October 1967 and September 1970, I wish to thank Professor T.S.West and Dr.R.M.Dagnall for their help and encouragement, without which this work would not have been undertaken. I also wish to thank my colleagues at Imperial College and the photocopying departments of Imperial College and Pilkington Brothers for their aid in preparing this thesis. Finally I should like to thank the Welding Institute for the funds to carry out this study. ABSTRACT The first part of this work was concerned with the use of a ternary complex, formed by the sensitisation of the aluminium catechol violet complex with cetyltrimethylammon- ium bromide, for the determination of aluminium. A solvent extraction system was developed using benzoic acid in ethyl acetate to extract the aluminium away from a number of interfering species, principally iron and some divalent cations. The aluminium was then back-extracted into aqueous solution for subsequent determination. EDTA was used as a mass masking agent for small quantities of interfering cations. A number of other ternary complexes of the first-row transition elements with catechol violet and cetyltrimeth- ylammonium bromide were prepared for the first time. The extinction coefficients were measured and a preliminary investigation of the compositions was undertaken. It is suggested that the iron catechol violet cetyltri- methylammonium bromide complex is suitable for further deve- lopment as a spectro-photometric reagent. The middle section of this work was concerned with the development of a sensitive flame speotrophotometrie method for boron, using the emission from the B02 radical in an oxygen-hydrogen-nitrogen co-axial flame, The technique was found to depend for its sensitivity upon the anomalously high volatility of boric acid in abso- lute methanol to achieve an indirect nebuliser efficiency approaching 60%. The latter part of the work was concerned with the calculation of free atom concentrations of elements in a number of flames. The atomisation of boron in five analytical flames was studied using this method using a digital computer to gene- rate graphs of the dependence of atomisation upon flame stoichiometry. This computer technique was also used to study the anomalously low sensitivity of determination of zirconium in the nitrous oxide acetylene flame. Data for titanium were also generated as a comparison. The study showed that condensed zirconium carbide is formed in the fuel-rich flame, seriously reducing atomisa- tion. In fuel-lean flames zirconium oxide species occur to lower the atomisation. Potation Because of the limitations of the typeface used, the following notatiowhas been employed in this work. Temperature Temperaturos are generally written thus:- 2000K for 2000 degrees Absolute(Kelvin) 2000C for 2000 degrees Centigrade(Colsius) Contracted Notation for Numbers Large or very small numbers are generally written in the contracted form thus :- 1.0E-04 for 0.00010 (1.0 x 10-4 ) 2.3E+05 for 230,000 (2.3 x 105 ) (This notation is standard usage for computers with a limited typeface.) Contents Chapter Title Pages 1. An Absorption Spectrophotometric Technique for 1.1 - the Determination of Aluminium Employing Tern- 1.31 ary Complexes. 2. Further Investigation of Ternary Complex Systems 2.1 - for Solution Absorption Spectrophotometry. 2.18 A Flame Spectrophotometric Technique for the 3.1 - Determination of Boron. 3.32 Computer Calculations of Boron Free-Atom Concen- 4.1 - trations in Analytical Flames. 4.78 Computer Calculations of Titanium and Zirconium 5.1 - Free-Atom Concentrations in the Nitrous Oxide 5.34 Acetylene Flame. Appendix A Digital Computer Program to Determine Species A.1 Concentrations by the Minimisation of Free A.25 Energy Total 218 pages CHAPTER AN ABSORPTION SPECTROPHOTOMETRIC TECHNIQUE FOR THE DETER- MINATION OF ALUMINIUM EMPLOYING TERNARY COMPTRXES. 1.1 introduction. The use of ternary complexes in analytical chemistry is well established for a great number of applications. These applications may be divided into two main types; those where the ternary complex is formed to be extracted with later determination of one of the components, not necessar- ily the analyte, and those where the ternary complex is determined speotrophotometrically. Examples of the first type are;the determination of boron by formation of barium borotartrate followed by deter- 1 mination of the barium either_ by flame photometry or X-ray fluorescence 2, and the determination of niobium by formation of molybdenum blue from the ternary phosphotoly- bdate 3. Examples of the second type are much more numerous including the determination of molybdenum and antimony 4, tin 5,6 , silver ', rare earths et fluoride 9,10, and the classical determination of phosphorus as phosphomolybdate. BAILEY 11 has subdivided the types of ternary complexes into five categories depending on the nature of each of the three components. These categories aree 1. complex anions - or SbC1 - which form colored complex products such as Fen4 6 with cationic chromophores such as triphenylmethane dyestuffs. or with other cations to form complexes suitable for the determination of the cation. 2. complexes of cations and complex mixed ligands such as phosphomolybdate. 3. complexes between a cation and two anionic ligands. 4. complexes Made by the combination of a cation, an anion, and an uncharged species such as 1,10 phenanthroline. 5. complexes formed in the presence of and modified by micellar aggregates. 1.2 The ternary complexes investigated in this study form part of the fifth category. A further three-way categorisation is possible. Ternary complexes used for absorption spectrophotometry may be considered as having one of three origins of colour form- ation. First the colour may be totally characteristic of one of the components,for example the ion association prod- ucts formed by the reaction of tetrafluoborate with Crystal. Violet 12, or Brilliant Green 13 Inthese techniques, the complex is normally extracted from unreacted reagent. Nearly all elements forming anionic complexes in highly acid solu- tions may be determined this way. Second, the colour may be totally unrelated to the colour of any of the components, usually due to a charge transfer mechanism.e.g. Cu(I) neocuproin nitrate 14. Third, the colour may be formed as a modification of the original colour of one of the complex components. This group includes the cerium/lanthanum fluoride Alizarin system 10, the Xylenol Orange rare earth cetylpyridinium bromide system 8, and the Catechol Violet metal surfactant system. In this latter system, the metal may be almost any cation and the surfactant may be any cationic one such as cetyltrimethylammonium salts or gelatine. The system selected for this study was the one of Catechol Violet(CV) and cetyltrimethylammonium bromide(CTAB) with various cations. Cateehol Violet was initially prepared as a metallo- chromic indicator principally for complexometric titrationa of such metals at; Co,Ni,Mn,Zn,Mg,Cd 15, Cu 16, Bi 17. 1.3 Because of its structure(Fig.1.1) with two complexing nuclei, it is extremely useful for this purpose and will give com- plexes with a large number of metals. Its use as a colorimetric reagent for a variety of metals has since been described. It is especially useful as a reagent for polyvalent metals and a number of methods for 18,19,20,21 zirconiUM , molybdenum,tungsten and vanadium 22, bismuth 23,24, anti titanium 25. This list is not exhaustive merely representative and many more references are available. Few references to its use for determining divalent metals are available, the reasons being that it is unstable in alkaline solution at the point of maximum formation of those complexes, and it not a very selective reagent. One 26 reference to its use for copper states that Pb,Ag,Hg,Bi, Zn,Sn,Sb,Ni,Cr,Fe,Mg,Ca,Sr,Ba all interfere so that it is only suitable for pure solutions. Further the determination must be carried out in neutral solution and is not very sen- sitive. More recently, the effect of dispersing agents such as gelatine and CTAB has been reported as giving improved sens- itivity, and several methods for various metals have been 4,5,6 published . A characteristic of the complex under the conditions used by these authors is the bathochromie shift in the wavelength of maximum absorbance. This shift has been attributed to the reaction of the various basic functional groups within the gelatine with the remaining acidic protons on the CV nucleus.26 The object of this research was to continue the invest- igation into this effect to elucidate the exact mechanism and develop analytical methods based upon it. The point of 1.4 commencement of this study was the observation of the form- ation of an aluminium-CV-CTAB complex during an earlier study 4. komaratu The apparatus used for this study consisted of a Unica* SP600 visible spectrophotometer with matched 1cm qua- rts curettes. For easier plotting of spectra, use was also made of a Unitas SP800 and a Beckmann DB600 scanning spectr- ophotometers. Reagents Al stock 0.0011 0.2267g of A.R. NH4A1(SO4)2.12H20 dissolved in 500m1 distilled water. C, 0.001M 0.1932g of CV dissolved in 500m1 distilled water CTAB 0.0011 0.36447g CTAB dissolved'in 1 litre distilled water Mixed Reagent 0.1546g CV & 1.458g CTAB dissolved in 2 litres distilled water 010 Buffer 5041 cone NH3 solution diluted to 350 ml, pH adjusted to40.2 with cone HO1 and diluted to 400m1.
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